1. Field of the Invention
This invention relates, generally, to solid state lighting devices. More particularly, it relates to a solid state lighting device that provides warm white light with a high color rendering index at a high luminous efficacy.
2. Description of the Prior Art
The development of warm white solid state lighting devices having high efficiency has been restricted because a warm white light device with a high color rendering index (CRI) requires more long wavelength spectrum light, which is less sensitive to a human eye, thereby resulting in a low brightness light. Conventional high color rendering warm white light devices require more power than devices with a low color rendering index and such increased power produces device-debilitating heat.
There is a need for a solid state lighting device having a high color rendering index that consumes a relatively low amount of power so that it is not subjected to debilitating heat.
The current state of the art includes LEDs having a luminous efficacy of about 100˜120 lm/W for cool white light (5000K˜6500K) at a CRI of 60˜75 and about 70˜85 lm/W for warm white light (2700K˜3000K) at a CRI of about 80 at 350 mA.
There is a need for an LED light source having a luminous efficacy above 100 lm/W at 350 mA for warm white light at a CRI of about 90. This would represent an improvement of more than forty percent (40%) over what a conventional phosphor converted warm white LED can achieve.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the art how such a lighting device could be provided.